Traveling through Asia this week, Trump's top aides insisted the meddling must be addressed if the two leaders met. Secretary of State Rex Tillerson told reporters in Beijing that the long list of topics up for discussion with Putin included the cyber-intrusion.

Trump, however, appeared ready to move on. He told reporters as he jetted here from the seaside Vietnamese resort in Da Nang that he accepted the Russian President's denials as sincere and stressed how insulted Putin feels when the issue is raised.

It's a conundrum Trump faces as investigators in Washington inch closer to his inner circle in their Russia probe. Deeply sensitive at the implication the Russian intrusion makes him appear illegitimate, Trump has been unable so far to say definitively whether Putin and his government was behind it.

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The unanswered question has left the matter unresolved -- and largely forestalled the type of substantive deliberations that Trump himself maintains are essential.

"I want to be able -- because I think it's very important -- to get along with Russia, to get along with China, to get along with Vietnam, to get along with lots of countries, because we have a lot of things we have to solve," Trump said during a news conference here on Sunday. "I feel that having Russia in a friendly posture, as opposed to always fighting with them, is an asset to the world and an asset to our country, not a liability."

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Standing in blue silk shirts provided by their hosts, Trump and Putin shook hands in Da Nang but never sat down for formal talks in Vietnam about Syria or North Korea -- two areas Trump has said repeatedly require Russian cooperation.

The prospects for a bilateral meeting were dampened by many factors, including disagreements over Russia's role in fueling the bloody Syrian civil war. But the issue of election meddling loomed as the investigation led by special counsel Robert Mueller proceeds apace.

The week before Trump departed on his diplomatic tour of Asia, three of Trump's former campaign aides were caught up in the probe -- two were indicted on the Monday ahead of Trump's departure and a third pleaded guilty and was revealed to be cooperating with investigators.

Book-ending Trump's trip jetting between Asian capitals, aides have been speaking with Mueller's team. Top policy adviser Stephen Miller -- who is traveling with the President in Asia -- spoke with Mueller before he departed. Hope Hicks, another aide on the road with Trump, is due to speak with Mueller when she returns.

As Trump departed Da Nang without meeting Putin, he fumed to reporters aboard Air Force One that intelligence officials from the last administration were "political hacks" and labeled the Russia investigation a "hit job" masterminded by Democrats.

Waking up in Hanoi, he unleashed a stream of invective on Twitter after remaining largely calm on social media all week, calling those who question his ties to Russia "haters and fools."

The response back in Washington was heated. Sen. John McCain, who was imprisoned during the Vietnam War less than a mile from where Trump was staying, wrote: "Vladimir Putin does not have America's interests at heart. To believe otherwise is not only naive but also places our national security at risk."

No direct answer

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Trump modulated his tone standing outside the mustard-hued presidential palace in Hanoi, saying that he sided with US intelligence agencies, who determined months ago that Russia was behind the interference.

But asked directly whether Russia was responsible for the meddling, he skirted the question again and avoided putting the matter to rest.

"As to whether I believe it or not, I am with our agencies, especially as currently constituted with the leadership," he said.

His grudging, caveated acceptance of a finding the US intelligence community arrived at months ago put him closer to the position of most of those in his administration. But it stopped short of answering the direct question he was posed about whether Russia was responsible.

In polling, Americans increasingly see the Russian meddling as a grave issue. In a CNN survey conducted this month, about two-thirds (64%) now say the investigation into Russian efforts to influence the US presidential election in 2016 is a serious matter that should be fully investigated, while just 32% see it as an effort to discredit Trump's presidency.

The percentage who say it's a "crisis" for the United States if the Russian government did attempt to influence the outcome of the presidential election now stands at 22%.

Trump's willingness to confront Putin will be tested in the coming months. Trump is required to impose new sanctions on Russian entities by January 29 under a law passed by Congress over the summer. The same law required the administration to identify targets for the sanctions by the beginning of last month; the roster of targets arrived three weeks late.

In his remarks on Sunday, Trump suggested that imposing new sanctions on Russia was misguided.

"People don't realize Russia has been very, very heavily sanctioned," Trump said. "They were sanctioned at a very high level, and that took place very recently. It's now time to get back to healing a world that is shattered and broken."